Poly(N-isopropylacrylamide) (PNIPAM) is well known to be sensitive to temperature, chemical species and concentrations. At low temperatures for example, the polymer has an extended chain configuration and is soluble in aqueous solvent. Above the lower critical solution temperature (LCST˜32° C.), the polymer folds and precipitates from solution. The process is driven by increased entropy in the system. Below LCST, water molecules align along the extended chain of the polymer. As PNIPAM becomes folded when the temperature is above LCST, these organized water molecules are lost to the bulk with less ordered structures, increasing the total entropy of the system. The chemical species in various solutions can interfere with the interaction between water and polymer molecules and influence the PNIPAM phase transition. This property has made PNIPAM based materials desirable in the field of surface chemistry, catalysis, and biotechnology. In surface chemistry, for instance, PNIPAM has been used to construct a “smart” surface whose hydro-phobicity varies with temperature. This endows the self-cleaning property of a surface that repels aqueous contaminants above phase transition temperatures. Due to the simple structure, facile synthesis and easily accessible transition temperature (32° C.) of PNIPAM, the clouding process has become a model system to study protein cold denaturation, which shares a similar phase transition mechanism. Such broad applicability of PNIPAM implies profound impacts on many fields once a new property associated with the polymer is discovered. Crosslinked PNIPAM in a form of sol gel has been found to respond to radiation pressure.
U.S. Pat. No. 5,095,515 relates to an optical switch which comprises a photoelastic, optically transparent material whose index of refraction is changed by stress and which propagates an optical beam or beams from an inlet window to an outlet window in the material, with the inlet window adapted to receive an optical beam from an optical source and the outlet window adapted to pass an optical beam from the photoelastic material to an optical output receptor, and a receptor means of applying a stress gradient to said photoelastic material to change the index of refraction and hence, the optical path of the optical beam between a normal, unstressed optical beam path and a bent, stressed optical beam path. Optical systems are described in which the optical switch is reportedly employed to form optical lenses wherein an optical beam is focused by stress within an optical material, such as a photoelastic cylindrical rod. Optical integrated systems are also described employing the optical switch with optical devices as an optical integrated module.
U.S. Pat. No. 5,368,781 relates to a reportedly tunable, radiation filter comprising a highly ordered crystalline array of microparticles fixed in a polymerized hydrogel.
U.S. Pat. No. 6,014,246 relates to devices that comprise, mesoscopically periodic materials that combine crystalline colloidal array (CCA) self-assembly with the temperature induced volume phase transitions of various materials, preferably poly(N-isopropylacrylamide) (PNIPAM). In one embodiment, a PNIPAM CCA is formed in an aqueous media and contained within cell means. In another embodiment, a CCA of charged particles is formed and polymerized in a PNIPAM hydrogel. Methods for making these devices are also disclosed. The devices of the present invention are reportedly useful in many applications including, for example, optical switches, optical limiters, optical filters, display devices and processing elements. The devices are further reportedly useful as membrane filters. All of these devices reportedly have the feature of being tunable in response to temperature. Devices that reportedly change diffracted wavelength in response to mechanical pressure are also disclosed.
U.S. Pat. Nos. 6,097,530 and 6,165,389 relate to devices that comprise, mesoscopically periodic materials that reportedly combine crystalline colloidal array (CCA) self-assembly with the temperature induced volume phase transitions of various materials, preferably poly(N-isopropylacrylamide) (PNIPAM). In one embodiment, a PNIPAM CCA is formed in an aqueous media and contained within cell means. In another embodiment, a CCA of charged particles is formed and polymerized in a PNIPAM hydrogel. Methods for making these devices are also disclosed. The devices are reportedly useful in many applications including, for example, optical switches, optical limiters, optical filters, display devices and processing elements. The devices are further reportedly useful as membrane filters. All of these devices reportedly have the feature of being tunable in response to temperature. Devices that change diffracted wavelength in response to mechanical pressure are also disclosed.
There is a widespread application of lasers in daily life and in the military, such as on the battlefield. People routinely use lasers for scientific or business presentations, alignment in constructions and various entertaining purposes. On the battlefield, lasers have already been deployed to detonate explosive devices and destroy reconnaissance instruments containing optical components. Human vision can be irreversibly damaged by lasers, especially at infrared wavelengths to which eyes are not sensitive and, therefore, “blinking protection” is absent. Recent incidents include a Delta pilot who was hit in the eye by a laser beam while flying a 737 and a 20 year-old intern at Los Alamos National Lab who was blinded by a laser beam. It is imperative to construct devices to protect human vision and optical instruments that are vulnerable to laser light or radiation at high intensities. Some devices available today adopt passive mechanisms where there exists little discrimination against laser intensities across the device aperture that admits the light. As a result, imaging field is narrower and the sensitivity to the light at normal intensities suffers. Although optical limiters can respond to a laser beam according to its intensity, the spectrum in wavelength is limited.
In view of the above, it would be desirable to provide protective compositions, and to construct a device including such compositions to protect vision and optical instruments that are vulnerable to lasers at relatively high radiation pressure.